This invention relates to an adaptive equalizer for improving the quality of digital data contained in an electrical input signal supplied to the equalizer. The equalizer compensates for amplitude and delay distortion affecting the quality of the digital data contained in the electrical input signal.
Adaptive or automatic equalizers are known in the prior art and are described in U.S. Pat. Nos. 3,375,473 to Lucky, 3,746,989 to Heim and 3,787,762 to Sato. In the system described in the Lucky patent, test pulses are utilized to arrive at optimum settings of attenuators in an equalizer that is responsive to the digital test pulses. The system described in the Heim patent perturbs the transmission path to permit determination of the best equalizer setting. Heim uses a quality detector that includes a DC level shifter and a half-wave rectifier to provide equalizer adjustments. The Sato patent describes an equalizer for a quadrature-amplitude-modulated signal. Of the systems mentioned above, it is believed that the Heim patent is most pertinent to the present invention. However, the Heim system is limited to frequency-shift-keyed signals and operates in a manner quite different than that described in the present invention.